Abrupt Changes in the Rate of Andean Plateau Uplift from Reversible Jump Markov Chain Monte Carlo Inversion of River Profiles

Abstract:

Constraints on the rate of surface uplift of the Central Andean Plateau provide important boundary conditions for regional geodynamic models and paleoclimate reconstructions. Here we present a fully nonlinear inverse method to extract the rock uplift history of the Central Andean Plateau from the Cotahuasi River and its tributaries. Our approach is based on an analytical solution to the stream power model that relates elevation to rock uplift history. We use a Bayesian inverse method, which allows us to quantify the complete posterior probability distribution of model parameters. However, an “erosional efficiency” defines the landscape response time, which must be determined using independent data. Therefore, we use thermochronometric data from the Cotahuasi Canyon, which record rapid fluvial incision at approximately 13-10 Ma, to calibrate our results and infer a rock uplift history for the north Central Andean Plateau. We find that rock uplift occurred between 25 and 10 Ma at rates as high as 0.25 km/Ma. The rock uplift rates inferred during this time are not as high as is predicted if the Central Andean Plateau grew in response to loss of unstable lithospheric mantle. Therefore, our results are more consistent with models that require gradual uplift of the Central Andean Plateau.